Los Angeles -LRB- CNN -RRB- -- The illness that derailed Miley Cyrus ' U.S. tour in April has returned like a wrecking ball at the start of her European tour .

Cyrus ' Friday and Saturday shows in Amsterdam and Antwerp have been rescheduled for June 20 and 22 because she suffered a setback in her battle against a `` severe allergic reaction '' to an antibiotic , her rep said .

The 21-year-old singer fell ill on April 15 and was kept in a Kansas City hospital for several days . The remaining North American shows in her `` Bangerz '' tour were postponed until August .

`` After a period of improvement , Cyrus ' symptoms have returned and doctors will not permit her to travel , '' her representative told CNN Wednesday . `` This type of extreme reaction can last up to 27 days and Cyrus must remain under doctors ' care at this time . ''

Cyrus is still hoping to perform her `` Bangerz '' show at London 's O2 Arena on May 6 , the rep said .

She initially became ill in early April with a flu-like illness , which caused her to pull out of her Charlotte show . After being prescribed the antibiotic Cephalexin , her health woes grew when an allergic reaction to the drug left Cyrus hospitalized for more than a week , according to a statement from her representative earlier this month .

Cyrus used Twitter to express her sadness , posting a tweet of 132 crying emoticons Tuesday .

CNN 's Breeanna Hare and Carolyn Sung contributed to this report .

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Miley 's weekend shows in Amsterdam and Antwerp are rescheduled in June

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`` After a period of improvement , Cyrus ' symptoms have returned , '' rep says

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Cyrus still hopes to perform her `` Bangerz '' show at London 's O2 Arena May 6

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Postponed North American shows are set for first two weeks in August